There are a range of applications in which creation of true time delay is desired. True time delay refers to delays realized by actual propagation of light through a waveguide of length necessary to realize a specific transit time (the delay time) as opposed to a delay realized, for example, by recirculation of light through a closed path, such as in a resonator. These applications include the creation of synthetic filters and also applications in biodetection. While optical fiber waveguides can provide the largest possible delays, these devices suffer from being a filamentary structure that is neither compact in size nor can be readily fabricated into precise lengths having micron precision.
A semiconductor-based approach that uses precision lithography to form waveguides on a chip is highly desirable for true time delay devices. According to such approach, time delays can be precisely controlled through lithography and the economics of scale provided by chip-based processing can lower the cost of production. Furthermore, such chip-based, optical delays can be integrated with other optical and/or electronic devices.
However, current technology for creating such chip-based waveguides results in waveguides that have optical losses many orders of magnitude higher than for optical fiber waveguides. As a result, the corresponding time delays possible using these structures are many orders smaller in comparison to what is now possible using optical fibers.